[Cooper]

Hi,

I'm taking an introductory on organic lab. It's been a while since I took an organic lecture, so I'm a bit rusty. I have a few review questions I need help with (they may seem a bit random).

1. What makes benzene more volatile than toluene? I thought toluene would be more volatile, since benzene could base stack and compact more. Is it because the methyl of toluene is an EDG and creates a small polarity?

2. Which of the following molecules from the picture below (picture "#2") has the higher melting point? I was thinking the molecule with the several alcohols, since hydrogen bonding would be able to occur with the carbonyl. This would mean it takes more energy to separate the molecules into a liquid form.

3. The T vs. V (of distillate) diagram below (picture "#3") is a distillation curve for a pyridine (BP 115 C)/acetic acid (BP 118 C) mixture. What does the indicated area (1) represent? I was thinking this would be the distillate containing mostly acetic acid, since it is the higher of the two plateaus. The options are:

a. mostly acetic acid
b. mostly pyridine
c. a mixture of acetic acid and pyridine
d. the azeotropic mixture of acetic acid and pyridine
e. forerun

4. If the normal boiling point of a substance is 153 C, what's the boiling point at 100 torr? Is the answer just 153 C multiplied by 100/760? (see picture "#4" below)

Thanks for any help.

[mjc123]

Q4: Haven't you seen one of these diagrams before? They shouldn't be examining you on things you haven't been taught.
You take the point on the right hand curve at 100 torr, and draw a straight line from there to the normal boiling point (153°C) on the middle scale. Then extrapolate this line to intersect the left hand scale, and the value at that point is the boiling point at 100 torr.

Is the answer just 153 C multiplied by 100/760? (see picture "#4" below)

Have a think about this.
(i) If it was that simple, what would be the point of giving you the diagram?
(ii) It might be plausible (though in fact wrong) to think of multiplying the absolute temperature (in K) by 100/760, but why would you think you could do that with an arbitrary scale like °C? Is water at 20°C twice as hot as water at 10°C?
(iii) Do you know how vapour pressure in fact varies with temperature? It's not linear.

[Cooper]

I didn't think it was that simple, which is why I asked about it. I literally had no idea what to do with the figures and have never seen them before. Unfortunately, many professors do test on things they did not cover. Thanks for the help.

[billnotgatez]

Is any of the stuff not covered in class in your text book?
I know one professor tested on
1/3 on stuff covered in class and in text book
1/3 on stuff covered in text book only
1/3 on stuff covered in class only
Therefor you had to attend class and read the text to get a grade better than 67

[Cooper]

Is any of the stuff not covered in class in your text book?
I know one professor tested on
1/3 on stuff covered in class and in text book
1/3 on stuff covered in text book only
1/3 on stuff covered in class only
Therefor you had to attend class and read the text to get a grade better than 67

It's actually just a laboratory class, so there's no textbook and it's not mentioned in the manual at all. I actually doubt it will be on our quiz, because it was from a quiz four years ago. But still, they posted it as a review guide, so I figured it's better to know and not need it than not know and need it.

[Dan]

Picture 3 shows a nomograph - you should be able to find instructions on how to use it by googling "nomograph".